1. Field of the Invention
The present invention relates to monitoring of a vehicle catalytic converter during vehicle engine/exhaust warm-up to assess condition of the catalytic converter.
2. Description of Related Art
Modern automotive engines typically use a catalytic converter to reduce the exhaust gas emissions produced by the engine. Such converters operate to chemically alter the exhaust gas composition to help meet various environmental regulations governing tailpipe emissions. Several methods have been developed to monitor operability of the catalytic converter under steady state engine operating conditions. One method described in U.S. Pat. No. 5,544,481 uses a microprocessor to determine a ratio of signal output amplitudes of upstream and downstream exhaust gas oxygen sensors during steady state engine operation.
An object of the present invention is to provide method and apparatus for monitoring a catalytic converter during engine/exhaust warm-up (i.e. during non-steady state catalyst operation) in a manner to assess the current condition of the catalyst.
The present invention provides a method of monitoring a catalytic converter during engine warm-up (non-steady state catalyst operation) using signal outputs of first and second exhaust gas oxygen sensors located upstream and downstream, respectively, of the catalytic converter. In one embodiment, a change in the signal output (e.g. switching characteristics) of the downstream sensor relative to the signal output of upstream sensor during engine warm-up is used to estimate the catalyst light-off temperature. In an illustrative embodiment of the present invention, a length ratio of signal output amplitudes of the first and second exhaust gas oxygen sensors is determined by an engine microprocessor during engine (and catalyst) warm-up initiated by engine cold starting. The microprocessor determines a catalyst light-off temperature when a transition of the ratio occurs from a relatively high value (e.g. near 1) indicative of low catalyst oxygen storage to a relatively lower value (e.g. near 0) indicative of relatively high catalyst oxygen storage. The catalyst light-off temperature thus determined is compared to a stored reference catalyst light-off temperature that is indicative of a properly functioning (e.g. fresh) catalyst to assess the condition of the catalyst; e.g. the extent or degree of any catalyst degradation.
The above objects and advantages of the present invention will become more readily apparent from the following description taken with the following drawings.